1. Field of the Invention
This invention involves slow release delivery systems for use in the monitoring and the control of cotton boll weevils and other insects that over-winter or inhabit crop and nearby non-crop areas where host crops are present and not present.
2. Description of the Art
Boll weevils are coleopteran insects that feed on cotton plants; causing serious damage to the plants and reducing yield. As a consequence, multiple applications of insecticides are required to maintain populations below economically damaging thresholds. Boll weevils are generally found in cotton growing regions of North, Central, and South America.
All life stages except the adult stage are spent inside cotton squares or bolls. Male boll weevils release an aggregating pheromone after feeding on cotton squares and both males and females are attracted to this pheromone. In general, adult, over-wintered females feed for 3 to 7 days, mate with males and start laying eggs. Starting in the spring, females lay one egg per square, but at the end of the crop lay several in a boll. Each female usually lays an average of 150 eggs in her lifetime, each of which hatch in about three to five days. The resulting grubs or larvae feed about a week inside squares or bolls before changing into pupae; this stage lasts three to five days. Adults develop from pupae and cut their way out of squares or bolls. New adults feed from three to five days, mate, and begin laying eggs for the next generation. These cycles are repeated during the season until the cotton plants are either destroyed or killed by frost. It is estimated that a single pair of weevils, left uncontrolled, can generate up to two million offspring per year.
The boll weevil is a non-indigenous pest to the United States and there have been active programs to eradicate the boll weevil from the United States for more than twenty years. Currently there are about 12.5 million acres in active eradication programs, about four million acres in post-eradication programs and 300,000 acres in pre-eradication zones. The eradication programs have been financed by federal and state government funding and producer fees. Upon completion during the next 10 years, the total cost of these programs will have exceeded $2.5 billion. The eradication programs use special traps to monitor populations of boll weevils, to determine when cotton fields are to be treated with insecticide for killing boll weevils, and to eliminate very low populations of boll weevils. The traps typically include separate dispensers of Grandlure (a synthetic, four component version of boll weevil aggregation pheromone) to attract and dispensers of dichlorvos (DDVP) to kill trapped weevils. Dichlorvos prevents most of the weevils trapped in the capture cylinder of the trap from escaping and dead weevils are more easily tabulated when the trap is serviced than are live weevils.
Examples of boll weevil attractant compositions including Grandlure are described, for example, in U.S. Pat. No. 3,803,303. Grandlure has been used in combination with feeding stimulants, poisons and other compounds, in a variety of different types of devices, for example, those described in U.S. Pat. No. 4,027,420. Polymeric compositions for attracting boll weevils using a sex attractant in combination with polyethylene glycol and a toxicant such as p-dichlorobenzene are disclosed, for example, in U.S. Pat. No. 3,803,303. The contents of these patents are hereby incorporated by reference. Plant attractants such as caryophylline oxide and beta-bisabalol have been used in some of these devices, where the attractant is applied to cotton dental-rolls. Other controlled-release dispensers have been developed to give long-term release of Grandlure (McKibben and Davich, Environmental Entomology, 6(6):804-806 (1977). Volatile compounds present in the cotton plant have been shown to attract boll weevils, although not when they are diapausing. Grandlure has been used in combination with volatile compounds present in dead plan material, such as described in U.S. Pat. No. 6,183,733.
Examples of a cotton boll weevil trap suitable for use with this invention are described, for example, in U.S. Pat. No. 6,430,868. The content of this patent is hereby incorporated by reference.
The pheromone and dichlorvos dispensers should each be dated and replaced on a regular basis (each 7 to 28 days) throughout the growing season in traps that are deployed from 1 per acre to 1 per 10 acres. The labor required for replacing and disposing of each type of dispensers is a significant cost to eradication programs. In an average year of an active eradication program on 12,500,000 acres, an estimated 160 metric tons of spent dispensers are collected from traps for disposal in landfills.